Bitumen blasting process and blast reactor therefor

ABSTRACT

The undesirable and damaging reaction heat occurring during the blowing of asphalt is avoided by injecting water into the air inlet pipes of the reactor vessel heated by the hot asphalt surrounding them. During this, the superheated steam produced without expenditure is passed through the liquid asphalt, causing the removal of low molecular hydrocarbons formed during the blowing or stripping.

United States Patent Senolt et a1. Nov. 20, 1973 [54] BITUMEN BLASTING PROCESS AND 2,099,434 11/1937 Culbertson 208/6 BLAST REACTOR THEREFOR 2,991,241 7/1961 Renner 208/6 1,057,227 3/1913 Dubbs 208/6 [75] Inventors: Hans Senolt; Heinrich Tomaschko;

Georg Palvik, all of Vienna, Austria [73] Assignee: Osterreichische Mineralolverwaltung ggfiyg lzfgzgsi'giz z Aktlengesellschaft, Vienna, Austria Atmmey Holman & Stem [22] Filed: July 23, 1969 [21] Appl. No.: 843,970

' [57] ABSTRACT [30] Foreign Application Pnonty Dam The undesirable and damaging reaction heat occurring July 25, 1968 Austria A 7210/68 during the blowing of asphalt is avoided by injecting water into the air inlet pipes of the reactor vessel [52] US. Cl. 208/6 heated by the hot asphalt surrounding them During this the superheated steam produced expe -1- [58] Field of Search 208/6 diture is passed through h liquid asphalt causing the removal of low molecular hydrocarbons formed dur- [56] References Cited ing the blowing or stripping.

4 Claims, 1 Drawing Figure PAIENIEUNIJVZO Ian 3773.649

INVENTORS NAME HANS SENOLT ET AL.

ATTQQNG'YS BITUMEN BLASTING PROCESS AND BLAST REACTOR THEREFOR This invention relates to asphalt blowing. Asphalt is a very viscous liquid, consisting essentially of hydrocarbons, and is soluble in carbon disulphide. It is substantially non-volatile and softens gradually when heated. It is black or brown in colour and possesses waterproofing and adhesive properties. It is obtained principally by re'finery processes from petroleum oil, and is also found as a natural deposit or, in association with mineral matter as a component of naturally occuring asphalt.

Asphalt is a natural or artificial mixture of bitumen with a substantial proportion of solid mineral matter.

The known asphalt blowing process is used to produce mineral oil asphalt of a desired hardness from soft mineral oil distillation residues, which are termed soft asphalt. The process essentially consists of blowing air into soft asphalt placed in a blowing vessel so that the air becomes finely divided. The most favourable reaction temperature depends on the composition of the mineral oil distillation residue introduced, but is generally about 250C. But since the blowing process is exothermic, the heat of reaction causes a rapid rise in the temperature of the material being treated so that the desired reaction temperature is exceeded which has a considerable detrimental effect on the quality of the end product. Too high temperatures lead in particular to the formation of carbonaceous material and carboids which are undesirable. lt'is therefore necessary to remove the heat of reaction from the asphalt.

The invention relates to a asphalt blowing process in which asphalt is cooled during a blowing process by injecting liquid water into an air stream and passing the air stream containing water through the asphalt. In the known processes of this kind suitable cooling of the asphalt can be achieved, but there is the disadvantage that, as a result of the high flow velocity in the air stream, which is generally 40-60 m/sec, the water introduced into the air stream may be carried along by the air stream in liquid form to the asphalt and when it moves into contact with the hot asphalt explosive evaporation of the water may occur and as this leads to irregularities in the treatment of the asphalt and sometimes the contents of the reactor foam over. Thisis particularly liable to happen if accumulations of water form at particular points in the blast air line and are then suddenly blown into the hot reaction material.

According to the invention these disadvantages are avoided or effectively reduced by evaporating the water in the air inlet tube which is surrounded by the asphalt before it is passed through the asphalt by extracting heat from the asphalt surrounding the tube so that the water reaches the asphalt in vapour form. In this manner, the cooling water reaches the asphalt together with the blowing air only in the form of water vapor. Thus there is no direct contact between hot asphalt and liquid water so that regular treatment of the asphalt can be achieved since the reaction temperature can be maintained constant at a desired value and without any significant variations, and foaming over of the asphalt is inhibited. The cooling is extremely efficient since at no point in the blowing air line is the temperature significantly below the reaction temperature so that the mobility of the asphalt is maintained and so consequently is heat transfer by natural convection. At

the same time the cooling is extremely economical as not only the thermal capacity of the water but the latent heat of evaporation, which is approximately seven times greater than the thermal capacity of the water, is used for the cooling. There is no danger of petrification of the cooling surfaces since the inner surfaces of the blowing air line are generally moistened with asphalt. it has been found to be particularly advantageous to reduce the flow velocity of the air stream'to 5 to 8 m/sec before the water is introduced. This velocity ensures complete evaporation of the water introduced into the air stream before'it reaches the asphalt and consequently the extraction of heat from the asphalt even if the length ofthe blowing air line in the blowing vessel is relatively small.

By means of the steam formed in the air injecting tube and fed into the asphalt the low-molecular hydrocarbons in the soft asphalt can be driven off so that again in this respect the process according to the invention is particularly advantageous. As is known, in the course of the asphalt blowing process'not only the desired high-molecular polymerisation products, such as asphaltenes, are formed, but also reaction by-products such as H O, CO and low-molecular hydrocarbons (blowing distillate) which are only partially able to escape with the exhaust air, a considerable part remaining in the asphalt whichresults both in slowing down the blowing process and in an impoverishment of the quality of the end product. Amongst other things, these reaction by-products lower the flash point and increase the loss on heating of the end product. The amount of superheated steam needed to drive off these undesired reaction by-products, that is for so-called stripping of the asphalt is about kg per ton of asphalt. In the case of the process according to the invention this requirement may be entirely covered by the cooling water evaporated in the air injecting tube and passed as steam through the asphalt so that it is unnecessary to provide additional steam to remove the byproducts. The superheated steam formed in the air injecting tube thus takes over the function of stripping, the latter being carried out particularly intensively since, for example, inthe case of a blowing vessel with a capacity of 40 tons-up to l 20kg of water per ton of asphalt can be introduced into the: blowing air line. Thus, by eliminating the otherwise necessary additional stripping steam, besides especially effective cooling there is also a considerable reduction in the low boiling oil fractions of the reaction material, which means concentration of the asphaltenes. Tests on the flash point and loss on heating" in the case of asphalt blown according to the invention give good results.

Furthermore the steam formed in the blowing air line and then passed through the asphalt reduces the oxy gen content of the exhaust air i.e., the air which has passed through the asphalt. When there is a high oxygen content of the exhaust air, the hydrocarbon vapours and mist in the exhaust air undergo reactions which can cause undesirable coking of exhaust air sysgives rise to additional costs and furthermore, in the case of intermittent operation, due to the formation of condensation can lead to the blowing vessel contents foaming over. In the process according to the invention the production and introduction of this additional blanketing steam is unnecessary. This has the advantage that the steam which has risen through the asphalt and been further heated by it is especially uniformly distributed in the exhaust air space since it escapes over the whole surface of the reaction material and thus there is a uniform reduction in the residual oxygen content in all regions of the exhaust air space. Thus the water fed to the blowing vessel and evaporated in the blowing air line is used not only for cooling, but in addition as stripper steam and also as blanketing steam.

The asphalt blowing vessel according to the invention for carrying out the process of the invention comprises a blowing vessel, a blast air line having a water inlet, the blowing air line at, and downstream of, the water inlet being of sufficient dimensions for all the water introduced into it to be evaporated. These dimensions can be determined empirically or by calculation without any difficulty for a particular case. It is of advantage if the air injecting line supplied with water has a greater flow cross-section than the part upstream of this so that the flow velocity of the air entraining the water is reduced from 40 to 60 m/sec to to 8 m/sec. To produce the required increase in the flow cross-section and also the cooling surfaces of the part of the blowing air line fed with water this part can take the form of several tubes in parallel, the total internal cross-section of which is greater than that of the blowing air line. The tubes can pass from an air distributing ring or manifold arranged above the blowing vessel through the blowing vessel to a gas distributor mounted in the region of the base of the blowing. Each tube may be provided with a separate water inlet.

The invention will be described in more detail with reference to the accompanying drawing which shows a longitudinal section through a blast reactor according to the invention.

The cylindrical blowing vessel is denoted by l, and an exhaust air line leaving the top of the vessel is denoted by 2. In the vessel base 3 there is an input aperture 4 through which a material to be treated, that is a soft mineral oil distillation residue for conversion into a mineral oil bitumen of a desired hardness, can be pumped into the reactor. The treated asphalt can be removed through an outlet 5 in the vessel base 3. A blowing air line 6 communicates with an air distributor ring or manifold 7. Leading from the distributor ring 7 are four parallel tubes 8 forming a blowing air injecting line A. Only three of these tubes 8 are shown in the drawing, one being partially broken away. The tubes 8 pass through the upper wall of the vessel and down through the vessel to a gas distributor 9, 9' in the base of the vessel. The distributor 9, 9' consists of a cylindrical part 9 and a disperser turbine 9'. Mouths 8 of the tubes 8 are directed towards the wall of the part 9. The disperser turbine 9' is driven by a motor 10. Shaft 11 of the motor carries a bevel gear 12 which meshes with a bevel gear 14 on turbine shaft l3. 15 shows the lower position of the turbine shaft 13 and 16 the upper position.

Each tube 8 is provided with a water feed pipe 17 to which the necessary quantity of water to keep the temperature constant is supplied by a dosing pump. The parts 8" of the tubes 8 to be fed with water have a total flow cross-section which is greater than that of the blowing air line 6. Thus the flow velocity of the blowing air in the parts 8" is less than that in the blowing air line 6. The cooling surfaces of the part 8" of the blowing air line A fed with water is considerably increased by distributing the total flow cross-section amongst the tubes 8. In the blowing vessel 1 the blowing air injecting line formed by these tubes is of dimensions sufficient to evaporate all the water fed into them, these dimensions being determined empirically or by calculation taking into account the respective given or desired behaviour.

Air is fed through the blowing air line 6 to the blasting at a speed of about 40-60 m/sec. This air is distributed by the air distributor or manifold ring 7 to the four tubes 8 forming the blowing air line A, and in which the flow velocity is reduced to about 5-8 m/sec. Water is sprayed into the tubes 8 through the water lines 17, is entrained by the air and is completely evaporated within the blowing air line surrounded by the hot asphalt in the blowing vessel. Due to the large heat of evaporation, the corresponding heat removed from the asphalt is considerable so that with a relatively small amount of water there is intensive cooling of the asphalt to control the desired reaction temperature. The superheated steam entrained by the air blast escapes into the asphalt through the tube mouths 8 together with the air blast, is deflected by the cylindrical part 9 to the disperser turbine 9' and, like the air, is dispersed in fine bubbles which rise through the asphalt. The steam is thus still further superheated by the hot asphalt and thus achieves especially intensive stripping, that is practically complete blowing off of undesired reaction by-products, in particular low-molecular hydrocarbons, which would detrimentally affect the quality of the end product and in addition slow down the blowing process. The foaming over of the blowing vessel is inhibited since water only enters the blowing contents in the form of steam. The steam then very uniformly distributed over the surface of the asphalt takes over the function of the previously used blanketing steam, that is the steam reduces the percentage residual oxygen content of the waste gases collecting in the waste air space to be removed through the air discharge pipe 2. Since'the superheated steam'cannot contain any water in liquid form, foaming over of the blowing vessel contents is inhibited by the saturated blowing steam.

The water fed to the tubes 8 is thus used not only for especially efficient cooling of the blowing vessel contents, but also for stripping and in addition for the nec-' essary dilution of the waste air.

We claim:

1. A process for blowing asphalt contained in molten form in a blowing vessel, said blowing vessel having blowing tubes having an inlet end and an outlet end, said outlet end being operatively connected to a gas distributor, said gas distributor being located in the region of the base of said vessel and said tubes being at least partially submerged in said asphalt to thereby be in heat exchange relationship with said asphalt, and a water feed pipe being connected to each of said tubes in the region of the inlet end thereof, said process comprising the steps of:

a. passing a stream of air through said tubes from the inlet end to the outlet end thereof;

b. introducing water into said stream of air through said water feed pipe, whereby said water is completely vaporized to steam within said tubes by extracting heat from said asphalt surrounding said tubes; and

molecular weight hydrocarbons in the asphalt are driven off by said steam in said mixture of air and steam.

4. A process according to claim 1, wherein the oxygen content of the air which has passed through the asphalt is reduced by said steam. 

2. A process according to claim 1, wherein the velocity of said air stream where said water is introduced into it is 5 to 8 m/sec.
 3. A process according to claim 1, wherein low-molecular weight hydrocarbons in the asphalt are driven off by said steam in said mixture of air and steam.
 4. A process according to claim 1, wherein the oxygen content of the air which has passed through the asphalt is reduced by said steam. 